The first 100% zoomed image (image # 2) was copied bit-by-bit from a portion of the full image with minimum compression by capturing the window content of a web browser. The full JPEG image loaded to the browser was generated from a NEF (raw) image. So, all the 36 megapixels from D800 were in use in the browser image.
The second JPEG image, on the other hand, is created from Lightroom after the original image was FIRST CROPPED to a similar area (769 x 437 pixels).
The difference between the images indicates that even with minimum compression setting (at least in Lightroom terms), a JPEG file loses some details - unless the details are lost by the browser. If this is not a browser problem, I guess the larger the image, the clearer the loss is when zoomed to 100%.
Yes, there is an additional screen-to-JPEG conversion from the screenshot; Nikonians does not support PNG files. Nevertheless, the difference was quite visible in the browser. It's easy to test: create a JPEG file from your sharpest image with minimum compression, load it to your web browser and compare it to the original image with 1:1 zoom factor.